/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.primitives;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkElementIndex;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkPositionIndexes;

import java.io.Serializable;
import java.util.AbstractList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.RandomAccess;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

/**
 * Static utility methods pertaining to {@code char} primitives, that are not
 * already found in either {@link Character} or {@link Arrays}.
 * 
 * @author Kevin Bourrillion
 * @since 2009.09.15 <b>tentative</b>
 */
@GwtCompatible
public final class Chars {
    private Chars() {
    }

    /**
     * The number of bytes required to represent a primitive {@code char} value.
     */
    public static final int BYTES = Character.SIZE / Byte.SIZE;

    /**
     * Returns a hash code for {@code value}; equal to the result of invoking
     * {@code ((Character) value).hashCode()}.
     * 
     * @param value
     *            a primitive {@code char} value
     * @return a hash code for the value
     */
    public static int hashCode(char value) {
        return value;
    }

    /**
     * Returns the {@code char} value that is equal to {@code value}, if
     * possible.
     * 
     * @param value
     *            any value in the range of the {@code char} type
     * @return the {@code char} value that equals {@code value}
     * @throws IllegalArgumentException
     *             if {@code value} is greater than {@link Character#MAX_VALUE}
     *             or less than {@link Character#MIN_VALUE}
     */
    public static char checkedCast(long value) {
        char result = (char) value;
        checkArgument(result == value, "Out of range: %s", value);
        return result;
    }

    /**
     * Returns the {@code char} nearest in value to {@code value}.
     * 
     * @param value
     *            any {@code long} value
     * @return the same value cast to {@code char} if it is in the range of the
     *         {@code char} type, {@link Character#MAX_VALUE} if it is too
     *         large, or {@link Character#MIN_VALUE} if it is too small
     */
    public static char saturatedCast(long value) {
        if (value > Character.MAX_VALUE) {
            return Character.MAX_VALUE;
        }
        if (value < Character.MIN_VALUE) {
            return Character.MIN_VALUE;
        }
        return (char) value;
    }

    /**
     * Compares the two specified {@code char} values. The sign of the value
     * returned is the same as that of {@code ((Character) a).compareTo(b)}.
     * 
     * @param a
     *            the first {@code char} to compare
     * @param b
     *            the second {@code char} to compare
     * @return a negative value if {@code a} is less than {@code b}; a positive
     *         value if {@code a} is greater than {@code b}; or zero if they are
     *         equal
     */
    public static int compare(char a, char b) {
        return a - b; // safe due to restricted range
    }

    /**
     * Returns {@code true} if {@code target} is present as an element anywhere
     * in {@code array}.
     * 
     * @param array
     *            an array of {@code char} values, possibly empty
     * @param target
     *            a primitive {@code char} value
     * @return {@code true} if {@code array[i] == target} for some value of
     *         {@code i}
     */
    public static boolean contains(char[] array, char target) {
        for (char value : array) {
            if (value == target) {
                return true;
            }
        }
        return false;
    }

    /**
     * Returns the index of the first appearance of the value {@code target} in
     * {@code array}.
     * 
     * @param array
     *            an array of {@code char} values, possibly empty
     * @param target
     *            a primitive {@code char} value
     * @return the least index {@code i} for which {@code array[i] == target},
     *         or {@code -1} if no such index exists.
     */
    public static int indexOf(char[] array, char target) {
        return indexOf(array, target, 0, array.length);
    }

    // TODO: consider making this public
    private static int indexOf(char[] array, char target, int start, int end) {
        for (int i = start; i < end; i++) {
            if (array[i] == target) {
                return i;
            }
        }
        return -1;
    }

    /**
     * Returns the start position of the first occurrence of the specified
     * {@code target} within {@code array}, or {@code -1} if there is no such
     * occurrence.
     * 
     * <p>
     * More formally, returns the lowest index {@code i} such that
     * {@code java.util.Arrays.copyOfRange(array, i, i + target.length)}
     * contains exactly the same elements as {@code target}.
     * 
     * @param array
     *            the array to search for the sequence {@code target}
     * @param target
     *            the array to search for as a sub-sequence of {@code array}
     */
    public static int indexOf(char[] array, char[] target) {
        checkNotNull(array, "array");
        checkNotNull(target, "target");
        if (target.length == 0) {
            return 0;
        }

        outer: for (int i = 0; i < array.length - target.length + 1; i++) {
            for (int j = 0; j < target.length; j++) {
                if (array[i + j] != target[j]) {
                    continue outer;
                }
            }
            return i;
        }
        return -1;
    }

    /**
     * Returns the index of the last appearance of the value {@code target} in
     * {@code array}.
     * 
     * @param array
     *            an array of {@code char} values, possibly empty
     * @param target
     *            a primitive {@code char} value
     * @return the greatest index {@code i} for which {@code array[i] == target}
     *         , or {@code -1} if no such index exists.
     */
    public static int lastIndexOf(char[] array, char target) {
        return lastIndexOf(array, target, 0, array.length);
    }

    // TODO: consider making this public
    private static int lastIndexOf(char[] array, char target, int start, int end) {
        for (int i = end - 1; i >= start; i--) {
            if (array[i] == target) {
                return i;
            }
        }
        return -1;
    }

    /**
     * Returns the least value present in {@code array}.
     * 
     * @param array
     *            a <i>nonempty</i> array of {@code char} values
     * @return the value present in {@code array} that is less than or equal to
     *         every other value in the array
     * @throws IllegalArgumentException
     *             if {@code array} is empty
     */
    public static char min(char... array) {
        checkArgument(array.length > 0);
        char min = array[0];
        for (int i = 1; i < array.length; i++) {
            if (array[i] < min) {
                min = array[i];
            }
        }
        return min;
    }

    /**
     * Returns the greatest value present in {@code array}.
     * 
     * @param array
     *            a <i>nonempty</i> array of {@code char} values
     * @return the value present in {@code array} that is greater than or equal
     *         to every other value in the array
     * @throws IllegalArgumentException
     *             if {@code array} is empty
     */
    public static char max(char... array) {
        checkArgument(array.length > 0);
        char max = array[0];
        for (int i = 1; i < array.length; i++) {
            if (array[i] > max) {
                max = array[i];
            }
        }
        return max;
    }

    /**
     * Returns the values from each provided array combined into a single array.
     * For example, {@code concat(new char[] a, b}, new char[] {}, new char[]
     * {c}} returns the array {@code a, b, c} .
     * 
     * @param arrays
     *            zero or more {@code char} arrays
     * @return a single array containing all the values from the source arrays,
     *         in order
     */
    public static char[] concat(char[]... arrays) {
        int length = 0;
        for (char[] array : arrays) {
            length += array.length;
        }
        char[] result = new char[length];
        int pos = 0;
        for (char[] array : arrays) {
            System.arraycopy(array, 0, result, pos, array.length);
            pos += array.length;
        }
        return result;
    }

    /**
     * Returns a big-endian representation of {@code value} in a 2-element byte
     * array; equivalent to
     * {@code ByteBuffer.allocate(2).putChar(value).array()}. For example, the
     * input value {@code '\\u5432'} would yield the byte array {@code 0x54,
     * 0x32} .
     * 
     * <p>
     * If you need to convert and concatenate several values (possibly even of
     * different types), use a shared {@link java.nio.ByteBuffer} instance, or
     * use {@link com.google.common.io.ByteStreams#newDataOutput()} to get a
     * growable buffer.
     */
    @GwtIncompatible("doesn't work")
    public static byte[] toByteArray(char value) {
        return new byte[] { (byte) (value >> 8), (byte) value };
    }

    /**
     * Returns the {@code char} value whose big-endian representation is stored
     * in the first 2 bytes of {@code bytes}; equivalent to
     * {@code ByteBuffer.wrap(bytes).getChar()}. For example, the input byte
     * array {@code 0x54, 0x32} would yield the {@code char} value
     * {@code '\\u5432'}.
     * 
     * <p>
     * Arguably, it's preferable to use {@link java.nio.ByteBuffer}; that
     * library exposes much more flexibility at little cost in readability.
     * 
     * @throws IllegalArgumentException
     *             if {@code bytes} has fewer than 2 elements
     */
    @GwtIncompatible("doesn't work")
    public static char fromByteArray(byte[] bytes) {
        checkArgument(bytes.length >= BYTES, "array too small: %s < %s",
                bytes.length, BYTES);
        return (char) ((bytes[0] << 8) | (bytes[1] & 0xFF));
    }

    /**
     * Returns an array containing the same values as {@code array}, but
     * guaranteed to be of a specified minimum length. If {@code array} already
     * has a length of at least {@code minLength}, it is returned directly.
     * Otherwise, a new array of size {@code minLength + padding} is returned,
     * containing the values of {@code array}, and zeroes in the remaining
     * places.
     * 
     * @param array
     *            the source array
     * @param minLength
     *            the minimum length the returned array must guarantee
     * @param padding
     *            an extra amount to "grow" the array by if growth is necessary
     * @throws IllegalArgumentException
     *             if {@code minLength} or {@code padding} is negative
     * @return an array containing the values of {@code array}, with guaranteed
     *         minimum length {@code minLength}
     */
    public static char[] ensureCapacity(char[] array, int minLength, int padding) {
        checkArgument(minLength >= 0, "Invalid minLength: %s", minLength);
        checkArgument(padding >= 0, "Invalid padding: %s", padding);
        return (array.length < minLength) ? copyOf(array, minLength + padding)
                : array;
    }

    // Arrays.copyOf() requires Java 6
    private static char[] copyOf(char[] original, int length) {
        char[] copy = new char[length];
        System.arraycopy(original, 0, copy, 0,
                Math.min(original.length, length));
        return copy;
    }

    /**
     * Returns a string containing the supplied {@code char} values separated by
     * {@code separator}. For example, {@code join("-", '1', '2', '3')} returns
     * the string {@code "1-2-3"}.
     * 
     * @param separator
     *            the text that should appear between consecutive values in the
     *            resulting string (but not at the start or end)
     * @param array
     *            an array of {@code char} values, possibly empty
     */
    public static String join(String separator, char... array) {
        checkNotNull(separator);
        int len = array.length;
        if (len == 0) {
            return "";
        }

        StringBuilder builder = new StringBuilder(len + separator.length()
                * (len - 1));
        builder.append(array[0]);
        for (int i = 1; i < len; i++) {
            builder.append(separator).append(array[i]);
        }
        return builder.toString();
    }

    /**
     * Returns a comparator that compares two {@code char} arrays
     * lexicographically. That is, it compares, using
     * {@link #compare(char, char)}), the first pair of values that follow any
     * common prefix, or when one array is a prefix of the other, treats the
     * shorter array as the lesser. For example,
     * {@code [] < ['a'] < ['a', 'b'] < ['b']}.
     * 
     * <p>
     * The returned comparator is inconsistent with
     * {@link Object#equals(Object)} (since arrays support only identity
     * equality), but it is consistent with
     * {@link Arrays#equals(char[], char[])}.
     * 
     * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order">
     *      Lexicographical order</a> article at Wikipedia
     * @since 2010.01.04 <b>tentative</b>
     */
    public static Comparator<char[]> lexicographicalComparator() {
        return LexicographicalComparator.INSTANCE;
    }

    private enum LexicographicalComparator implements Comparator<char[]> {
        INSTANCE;

        public int compare(char[] left, char[] right) {
            int minLength = Math.min(left.length, right.length);
            for (int i = 0; i < minLength; i++) {
                int result = Chars.compare(left[i], right[i]);
                if (result != 0) {
                    return result;
                }
            }
            return left.length - right.length;
        }
    }

    /**
     * Copies a collection of {@code Character} instances into a new array of
     * primitive {@code char} values.
     * 
     * <p>
     * Elements are copied from the argument collection as if by
     * {@code collection.toArray()}. Calling this method is as thread-safe as
     * calling that method.
     * 
     * @param collection
     *            a collection of {@code Character} objects
     * @return an array containing the same values as {@code collection}, in the
     *         same order, converted to primitives
     * @throws NullPointerException
     *             if {@code collection} or any of its elements is null
     */
    public static char[] toArray(Collection<Character> collection) {
        if (collection instanceof CharArrayAsList) {
            return ((CharArrayAsList) collection).toCharArray();
        }

        Object[] boxedArray = collection.toArray();
        int len = boxedArray.length;
        char[] array = new char[len];
        for (int i = 0; i < len; i++) {
            array[i] = (Character) boxedArray[i];
        }
        return array;
    }

    /**
     * Returns a fixed-size list backed by the specified array, similar to
     * {@link Arrays#asList(Object[])}. The list supports
     * {@link List#set(int, Object)}, but any attempt to set a value to
     * {@code null} will result in a {@link NullPointerException}.
     * 
     * <p>
     * The returned list maintains the values, but not the identities, of
     * {@code Character} objects written to or read from it. For example,
     * whether {@code list.get(0) == list.get(0)} is true for the returned list
     * is unspecified.
     * 
     * @param backingArray
     *            the array to back the list
     * @return a list view of the array
     */
    public static List<Character> asList(char... backingArray) {
        if (backingArray.length == 0) {
            return Collections.emptyList();
        }
        return new CharArrayAsList(backingArray);
    }

    @GwtCompatible
    private static class CharArrayAsList extends AbstractList<Character>
            implements RandomAccess, Serializable {
        final char[] array;
        final int start;
        final int end;

        CharArrayAsList(char[] array) {
            this(array, 0, array.length);
        }

        CharArrayAsList(char[] array, int start, int end) {
            this.array = array;
            this.start = start;
            this.end = end;
        }

        @Override
        public int size() {
            return end - start;
        }

        @Override
        public boolean isEmpty() {
            return false;
        }

        @Override
        public Character get(int index) {
            checkElementIndex(index, size());
            return array[start + index];
        }

        @Override
        public boolean contains(Object target) {
            // Overridden to prevent a ton of boxing
            return (target instanceof Character)
                    && Chars.indexOf(array, (Character) target, start, end) != -1;
        }

        @Override
        public int indexOf(Object target) {
            // Overridden to prevent a ton of boxing
            if (target instanceof Character) {
                int i = Chars.indexOf(array, (Character) target, start, end);
                if (i >= 0) {
                    return i - start;
                }
            }
            return -1;
        }

        @Override
        public int lastIndexOf(Object target) {
            // Overridden to prevent a ton of boxing
            if (target instanceof Character) {
                int i = Chars
                        .lastIndexOf(array, (Character) target, start, end);
                if (i >= 0) {
                    return i - start;
                }
            }
            return -1;
        }

        @Override
        public Character set(int index, Character element) {
            checkElementIndex(index, size());
            char oldValue = array[start + index];
            array[start + index] = element;
            return oldValue;
        }

        /** In GWT, List and AbstractList do not have the subList method. */
        /* @Override */public List<Character> subList(int fromIndex, int toIndex) {
            int size = size();
            checkPositionIndexes(fromIndex, toIndex, size);
            if (fromIndex == toIndex) {
                return Collections.emptyList();
            }
            return new CharArrayAsList(array, start + fromIndex, start
                    + toIndex);
        }

        @Override
        public boolean equals(Object object) {
            if (object == this) {
                return true;
            }
            if (object instanceof CharArrayAsList) {
                CharArrayAsList that = (CharArrayAsList) object;
                int size = size();
                if (that.size() != size) {
                    return false;
                }
                for (int i = 0; i < size; i++) {
                    if (array[start + i] != that.array[that.start + i]) {
                        return false;
                    }
                }
                return true;
            }
            return super.equals(object);
        }

        @Override
        public int hashCode() {
            int result = 1;
            for (int i = start; i < end; i++) {
                result = 31 * result + Chars.hashCode(array[i]);
            }
            return result;
        }

        @Override
        public String toString() {
            StringBuilder builder = new StringBuilder(size() * 3);
            builder.append('[').append(array[start]);
            for (int i = start + 1; i < end; i++) {
                builder.append(", ").append(array[i]);
            }
            return builder.append(']').toString();
        }

        char[] toCharArray() {
            // Arrays.copyOfRange() requires Java 6
            int size = size();
            char[] result = new char[size];
            System.arraycopy(array, start, result, 0, size);
            return result;
        }

        private static final long serialVersionUID = 0;
    }
}
